Rav Nahman was especially interested in correction for sexual sin which people had been interested in before him. Masturbation (spilling seed in vain) was the specific issue he was addressing, but the fact is that all sexual sin more or less come under the same heading.
The Ari, Isaac Luria, has a few unification for that purpose, but the thing about unifications is they depend on a precondition of attachment to the Divine. Without that they do nothing.
So R Nahman did his own prayer and and service towards God and received the idea of the Tikun HaKlali, i.e. the ten psalms to say that same day that one has sinned. That means the day starting at night and ending 24 hours later at 72 minutes after sun down.
The ten psalms are 16,32.41,42,59,77,90,105,137,150. (With intending the Divine Names אלף למד
אלף למד הי יוד מם)
What promotes this is that I see there is a lot of ignorance out there in terms of sexual issues.
So I thought to write a bit about it.
The main thing to know is that in Torah there are levels of how severe any particular sin is.
It starts with an איסור עשה, לאו, לאו שיש בו מיתת בית דין. The first level is a negative command derived from a positive command. Then straight negative commands. Then Negative commands that have the death penalty. Those are usually connected with when it says in the Torah "That soul will be cut off" but not always. It is useful to know this because it gives a simple way of knowing what the Torah considers more severe and what is less severe.
So one one hand we have the argument about a girl friend between the Rambam against all the other rishonim. But though to the Rambam a girl friend is forbidden it comes only as a negative derived from a negative. That is one is supposed to do Kidushin and then Hupa. [The other rishonim allow this but here I am just giving an example of where that category comes up.]
The next level is all the times it says in Torah do not do something but gives no punishment.
The next level is where there is a death penalty attached like in Leviticus 18 and 20. That includes homosexuality [Leviticus chapter 18: verse 22 and chapter 20 verse 13]. But those particular sins have an extra degree of severity because they come under the category of יהרג ואל יעבור, Be killed rather than transgress. That does not apply to any other commands except three: Idolatry, Murder, and the sexual acts of Leviticus 18 and 20.
I hope this short review is helpful for people. [I do quote Rav Nahman because I do not think he came under the (חרם) excommunication signed by the Gra.] That brings up this other issue about idolatry;- that was clearly the main reason the Gra signed the letter of excommunication. And that certainly still applies.
[Having a good idea of the actual legal status of any sin is helpful also, because a lot of times you find statement about the severity of some sin that gives you the impression that that is the worst of them all. Yet later you find that the legal status is nothing. So you know the previous statement was meant in a spiritual sense.]
Idolatry you know is severe for the reason that it is emphasized in the Torah itself. But also because it is the main thing that the prophets stress. What ever failings the kings of Judah may have had the prophets always stress only one point--did they or did they not do idol worship?